A light emitting device including a light emitting diode (LED) is used for lighting devices such as a liquid crystal display backlight, a signal device, various kinds of switches, a lamp for vehicles, and general lighting, for instance. In particular, a white light source composed of the combination of LED and a phosphor is drawing attention as a substitute for an incandescent light bulb, and for example, an LED light bulb having the same shape as that of the incandescent light bulb is known. The LED light bulb has, for example, an integrated lamp structure including a base portion, a lamp cap provided on the base portion, a globe, an LED chip disposed in the globe and having a white light emitting diode, and an LED chip lighting circuit provided in the base portion. In this case, the lamp cap is electrically connected to the base portion.
Brightness of an incandescent light bulb is adjusted according to user's preference. For example, when the brightness is adjusted to a darker side, an emitted light tends to be a reddish white light and also to have a lower color temperature due to an emission characteristic of a tungsten filament. The emission characteristic of the incandescent light bulb to thus vary in color temperature with brightness is unconsciously accepted by people, and accordingly a newly proposed light emitting device is required to have the same emission characteristic as that of the incandescent light bulb.
In the conventional light emitting device, however, it is difficult to vary brightness such as the total luminous flux as the color temperature of the white light varies, though the brightness of the white light is adjustable at the same color temperature. For example, in a conventional white light source which produces a white light by the combination of LED and a phosphor, even when the brightness of the LED is adjusted, the color temperature of the white light does not vary. Accordingly, in order to vary the emission color, changing the kind of the phosphor or the kind of the LED has been required.